tree: update reference to TypeScript bug (#21299)

## Description

microsoft/TypeScript#56718 was fixed, but does
not fix our issue so
microsoft/TypeScript#58688 was filed and is
now referenced.

Also a few minor cleanups in the file I saw while working on it.

Author: CraigMacomber

packages/dds/tree/src/simple-tree/schemaCreationUtilities.ts

@@ -41,7 +41,7 @@ export function singletonSchema<TScope extends string, TName extends string | nu
 
 	// Returning SingletonSchema without a type conversion results in TypeScript generating something like `readonly "__#124291@#brand": unknown;`
 	// for the private brand field of TreeNode.
-	// This numeric id doesn't seem to be stable over incremental builds, and thus causes diffs if the API extractor reports.
+	// This numeric id doesn't seem to be stable over incremental builds, and thus causes diffs in the API extractor reports.
 	// This is avoided by doing this type conversion.
 	// The conversion is done via assignment instead of `as` to get stronger type safety.
 	const toReturn: TreeNodeSchemaClass<
@@ -154,7 +154,7 @@ export function typedObjectValues<TKey extends string, TValues>(
 // eslint-disable-next-line @typescript-eslint/explicit-function-return-type
 export function enumFromStrings<TScope extends string, const Members extends string>(
 	factory: SchemaFactory<TScope>,
-	members: Members[],
+	members: readonly Members[],
 ) {
 	const names = new Set(members);
 	if (names.size !== members.length) {
@@ -182,7 +182,7 @@ export function enumFromStrings<TScope extends string, const Members extends str
 }
 
 // TODO: Why does this one generate an invalid d.ts file if exported?
-// Tracked by https://github.com/microsoft/TypeScript/issues/56718
+// Tracked by https://github.com/microsoft/TypeScript/issues/58688
 // TODO: replace enumFromStrings above with this simpler implementation when the TypeScript bug is resolved.
 // eslint-disable-next-line @typescript-eslint/explicit-function-return-type
 function _enumFromStrings2<TScope extends string, const Members extends readonly string[]>(